The vast majority of chicken owners do so (treat humanely). “Cruelty-free” and “humanely-treated” just sound like smoke and mirrors to me, if I were a customer, and as I said, I would wonder what else is made up.
Rather than come up with catchphrases, I like the suggestions that you put up photos of your flock in their home setting. It gives people a visual so they can see that these are well cared for animals, rather than just a claim that they are.
I remember someone on here saying they included a small slip of paper with their eggs with photos and stories about their chickens. I thought that was a cute way to help the customer connect to where the eggs come from.